The principal investigator wishes to exploit a novel computation procedure which he has developed for radiotherapy photon dose distributions. The technique has been implemented in a limited fashion on a small computer. Initial work with this procedure indicates that it holds promise as a means of realistically using CT data to carry out three-dimensional dose distribution calculations. The algorithm is closely wed to the use of the finitie fast Fourier transform to perform convolutions over a calculation volume. The fast Fourier transform (FFT) can be carried out most rapidly for large arrays using recent developments in array processors. Specifically, dose calculations over arrays having dimensions in the range of 64x64x64 to 128x128x32 elements will be manipulated in a 32 bit computer. The investigator will: (1) evaluate its ability to model dose due to inhomogeneities in three dimensions, and (2) reduce the time required to calculate dose distributions over a volume to clinically practical levels. The aim of the project will be to exhaustively define the limits of accuracy of algorithms that can be implemented using transform based convolutions. These algorithms consist of vector arithematic which is ideally suited for eventual implementation on array processors.